Update nbstripout requirement from ~=0.5.0 to ~=0.6.0
Updates the requirements on [nbstripout](https://github.com/kynan/nbstripout) to permit the latest version.
- [Release notes](https://github.com/kynan/nbstripout/releases)
- [Changelog](https://github.com/kynan/nbstripout/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/kynan/nbstripout/compare/0.5.0...0.6.0)
---
updated-dependencies:
- dependency-name: nbstripout
dependency-type: direct:development
...
Signed-off-by: dependabot[bot] <support@github.com>